In the related art, HFC refrigerant used in refrigerating machines and heat pumps has Global Warming Potential (GWP) of several hundred to several thousand and thus, it is necessary to switch from HFC refrigerant to HFO refrigerant (for example, HPO-1233zd of HPO-1234ze) having GWP less than 10. HFO-1233zd(E), which is not combustible, has a boiling point of approximately 18° C. Accordingly, in a case where HFO-1233zd(E) is used as a refrigerant for a refrigerating machine, a pressure in an evaporator becomes a negative pressure, and thus, entering of air into the refrigerating machine is concerned. If air enters the refrigerating machine, there is a concern that performance deterioration of the refrigerating machine is generated due to an increase in a condensation pressure and a failure and stopping of the refrigerating machine are generated due to an increase in abnormality. In addition, if water inside the refrigeration machine and oxygen of the entering air are combined to each other, there is a concern that rust occurs and the refrigerating machine (particularly, compressor) deteriorates.
As a technology for extracting a noncondensable gas such as air entering the refrigerating machine is known in PTLs below.